Re: [PATCH v2 net] net: sched: fix uses after free

[David Miller]

From: Eric Dumazet 
Date: Wed, 14 Mar 2018 18:53:00 -0700

> syzbot reported one use-after-free in pfifo_fast_enqueue() [1]
> 
> Issue here is that we can not reuse skb after a successful skb_array_produce()
> since another cpu might have consumed it already.
> 
> I believe a similar problem exists in try_bulk_dequeue_skb_slow()
> in case we put an skb into qdisc_enqueue_skb_bad_txq() for lockless qdisc.
 ...
> Fixes: c5ad119fb6c0 ("net: sched: pfifo_fast use skb_array")
> Signed-off-by: Eric Dumazet 
> Reported-by: syzbot+ed43b6903ab968b16...@syzkaller.appspotmail.com

Applied, thanks a lot Eric.

Re: [PATCH v2 net] net: sched: fix uses after free

[John Fastabend]

On 03/14/2018 08:10 PM, John Fastabend wrote:
> On 03/14/2018 06:53 PM, Eric Dumazet wrote:
>> syzbot reported one use-after-free in pfifo_fast_enqueue() [1]
>>
>> Issue here is that we can not reuse skb after a successful 
>> skb_array_produce()
>> since another cpu might have consumed it already.
>>
>> I believe a similar problem exists in try_bulk_dequeue_skb_slow()
>> in case we put an skb into qdisc_enqueue_skb_bad_txq() for lockless qdisc.
>>
> 
> [...]
> 
>> Fixes: c5ad119fb6c0 ("net: sched: pfifo_fast use skb_array")
>> Signed-off-by: Eric Dumazet 
>> Reported-by: syzbot+ed43b6903ab968b16...@syzkaller.appspotmail.com
>> Cc: John Fastabend 
>> Cc: Jamal Hadi Salim 
>> Cc:  Cong Wang 
>> Cc:  Jiri Pirko 
>> ---
>>  net/sched/sch_generic.c | 22 +-
>>  1 file changed, 13 insertions(+), 9 deletions(-)
>>
> 
> Thanks!
> 
> Acked-by: John Fastabend 
> 
>> diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
>> index 
>> 190570f21b208d5a17943360a3a6f85e1c2a2187..7e3fbe9cc936be376b66a5b12bf8957c3b601f2c
>>  100644
>> --- a/net/sched/sch_generic.c
>> +++ b/net/sched/sch_generic.c
>> @@ -106,6 +106,14 @@ static inline void qdisc_enqueue_skb_bad_txq(struct 
>> Qdisc *q,
>>  
>>  __skb_queue_tail(>skb_bad_txq, skb);
>>  
>> +if (qdisc_is_percpu_stats(q)) {
>> +qdisc_qstats_cpu_backlog_inc(q, skb);
> 
> So I guess the skb access above needs to be removed as
> well per your comment in the commit description. But that
> can be another patch.
> 

Actually this is fine I read this too quickly on first
read.

Sorry for the noise.  Looks good to me. 

>> +qdisc_qstats_cpu_qlen_inc(q);
>> +} else {
>> +qdisc_qstats_backlog_inc(q, skb);
>> +q->q.qlen++;
>> +}
>> +
>>  if (lock)
>>  spin_unlock(lock);
>>  }
> 
> 

Re: [PATCH v2 net] net: sched: fix uses after free

[John Fastabend]

On 03/14/2018 06:53 PM, Eric Dumazet wrote:
> syzbot reported one use-after-free in pfifo_fast_enqueue() [1]
> 
> Issue here is that we can not reuse skb after a successful skb_array_produce()
> since another cpu might have consumed it already.
> 
> I believe a similar problem exists in try_bulk_dequeue_skb_slow()
> in case we put an skb into qdisc_enqueue_skb_bad_txq() for lockless qdisc.
> 

[...]

> Fixes: c5ad119fb6c0 ("net: sched: pfifo_fast use skb_array")
> Signed-off-by: Eric Dumazet 
> Reported-by: syzbot+ed43b6903ab968b16...@syzkaller.appspotmail.com
> Cc: John Fastabend 
> Cc: Jamal Hadi Salim 
> Cc:   Cong Wang 
> Cc:   Jiri Pirko 
> ---
>  net/sched/sch_generic.c | 22 +-
>  1 file changed, 13 insertions(+), 9 deletions(-)
> 

Thanks!

Acked-by: John Fastabend 

> diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
> index 
> 190570f21b208d5a17943360a3a6f85e1c2a2187..7e3fbe9cc936be376b66a5b12bf8957c3b601f2c
>  100644
> --- a/net/sched/sch_generic.c
> +++ b/net/sched/sch_generic.c
> @@ -106,6 +106,14 @@ static inline void qdisc_enqueue_skb_bad_txq(struct 
> Qdisc *q,
>  
>   __skb_queue_tail(>skb_bad_txq, skb);
>  
> + if (qdisc_is_percpu_stats(q)) {
> + qdisc_qstats_cpu_backlog_inc(q, skb);

So I guess the skb access above needs to be removed as
well per your comment in the commit description. But that
can be another patch.

> + qdisc_qstats_cpu_qlen_inc(q);
> + } else {
> + qdisc_qstats_backlog_inc(q, skb);
> + q->q.qlen++;
> + }
> +
>   if (lock)
>   spin_unlock(lock);
>  }